I decided to nail the problem of KDE running very slowly with an NFS-mounted $HOME. This is a qualitative rather than quantitative test.

I tried with KDE with both a locally-mounted and a NFS-mounted $HOME. In both cases, $HOME/.kde4 was a symlink to /var/tmp/mounty/.kde4 which is on a local FS.

The performance of the NFS-mounted KDE was about an order of magnitude slower than with the local $HOME. For example, a kate session with NFS $HOME took so long to close that the 'this window is not responding' dialog appeared. With a local $HOME, kate closed instantly.

Building KDE with -semantic-desktop is not really feasible as the most useful applications (in my case, akregator) require +semantic-desktop._________________Michael Mounteney

The next step is to move more directories out of NFS-mounted $HOME and into local storage with symlinks from $HOME: .local/share/akonadi, .config/akonadi and .dbus but although it seems to make the system a little faster, there's still no breakthrough._________________Michael Mounteney

For some extremely good reason I'm sure, KDE deleted the symlink $HOME/.kde4 and replaced it with a directory. I'm sure it had a really good reason for doing so, but it prevented KDE from starting._________________Michael Mounteney